Mimosa oblonga

Title

Mimosa oblonga

Author(s)

Rupert C. Barneby

Scientific Name

Mimosa oblonga Benth.

Description

359. Mimosa oblonga Bentham, J. Bot. (Hooker) 4: 365. 1841.—Typus infra sub var. oblonga indicatur.

Stiff but slender, diffuse or assurgent, upwardly freely branched microphyllidious shrubs or subshrubs attaining 1-1.5 m, the brown or reddish stems at once gray-puberulent, densely hispid with divergent or sometimes distally recurved, rufous or yellowish setae to 0.5-3 mm, and armed on ribs usually remote from nodes with lustrous, gently recurved, broad-based or coarsely setiform aculei commonly to 1.5—4 mm, rarely smaller or exceptionally wanting, the olivaceous, when dry brownish, brittle lfts subconcolorous, either glabrous or thinly puberulent facially, finely discontinuously ciliate, the ellipsoid capitula single or geminate from all distal lf-axils on slender hispid peduncle, sometimes in praefloration shortly pseudoracemose. Stipules erect-incurved, lanceolate or lance-attenuate 1-7 x 0.2-0.5 mm, 1-nerved, dorsally puberulent, setose-ciliolate, persistent. Leaf-stalks either reduced to livid pulvinus or some developed and attaining 6 x 0.3 mm; pinnae 1-jug., the dorsally spreading-setose rachis of longer ones (8-) 10-3 5 mm, those of flowering branchlets often shorter than those of primary stem, the interfoliolar segments 0.4-1.1 (-1.3) mm; lfts of primary cauline lvs 1635-jug, of distal lvs fewer (no further described), decrescent near ends of rachis, the unequal first pair close to minute subulate paraphyllidia, all in outline linear to oblong, deeply obtusangulate at base, at apex obtuse, mucronulate or acute, those near mid-rachis 1.5-5.5 x 0.4-1.5 mm, 3-7.5 times as long as wide, weakly l-3(-4)-nerved from pulvinule, the midrib displaced to divide blade ±1:2-3, simple or faintly 1-2-branched distally, the inner posterior nerve ascending to beyond mid-blade, the outer one(s) much shorter, the venation prominulous only beneath, above immersed but sometimes discolored. Peduncles (7-) 10-35(-40) mm; capitula without filaments or emergent bracts 4-11 x 3-6 mm, 1.2-2.5 times as long as diam., the obovoid fl-buds either forwardly or retrorsely puberulent, prior to anthesis either shorter or longer than bracts, these elliptic-oblanceolate to linear, 0.5-3 mm, 1-nerved, setose-cili(ol)ate; flowers 4-merous 4-androus, in some capitula many or even all staminate; calyx membranous 0.15-0.5 mm, the obscurely lobulate or subtruncate rim either glabrous or minutely ciliolate; corolla turbinate or narrowly vase-shaped 1.3-2.2 mm, the ovate concave but scarcely thickened, 1-nerved lobes 0.5-0.8 x 0.35-0.6 mm, the tube glabrous to thinly retrostrigulose, the lobes more densely puberulent with variously oriented trichomes; filaments pink, free to base, exserted 3-5.5 mm. Pods 2-10 per capitulum, sessile, in profile oblong or oblong-elliptic 10-14 x 3 mm, 2-4-seeded, the replum 0.4-0.6 mm wide, hispid along back and sides with pluriseriate divaricate setae to 4-6 mm, the papery valves puberulent and thinly weakly setulose, when ripe breaking up into free-falling, individually dehiscent articles 2.5-4 mm long; seeds not seen ripe.

Mimosa oblonga is closely related to the extensively sympatric M. ramosissima, which is similar in growth-habit, foliage, and ecology, but is instantly separable by the relatively large firm 4-ribbed calyx with incurved deltate teeth, and less certainly by perfectly globose rather than ellipsoid capitula. As defined by the foregoing description M. oblonga is polymorphic in small differences of pubescence, armature, size of capitula, and length of floral bracts, but as some of this variation appears to be well correlated with dispersal it is possible to recognize two varieties.